My temp. guage in my '88 S/C, 305, used to never read any higher then 130 degress. A couple weeks ago I turned the heater on and the needle shot almost staright up. Now the needle won't move at all, and I get no temp. reading, it just stays all the way up, almost verticle. I have replaced my fan switch, temp. sensor, and thermostat, think I need a new temp gauge now, what do yall think?

 

What temp sensor did you replace? Was it the one right by the thermostat? If so that is the wrong switch, the one that controls your gauge is located in the drivers side head and has one single wire that goes directly to your gauge. This sensor is basically a variable resister, the hotter it gets the more resistance it has, so for instance if you unplug the wire and touch it to ground it will peg the needle hot and with no ground the needle will peg cold. The wire could be chaffed or cracked and ground out somewhere and cause it to peg hot. Dont know if this makes any sense to ya but it is the best way I can explain it.

I doubt the gauge is bad, they are just a coil spring inside with a hot wire and a ground, the ground goes to the sensor, the better ground it gets the hotter the wire gets and it uncoils causing the needle to move...kinda like the old round house thermostats.

 

I have replaced both the one near the thermostat and the one in the passenger side head, still the same roblem persists.

 

Your gauge is stuck there at the top. Happened to me, it's the wierdest thing. You have to remove the glass and push it down with your finger. I changed my coolant temp sensor and it doesn't peg to the top anymore. Yours I think works now but it's stuck.

 

I don't think the gauge is simply stuck. I took the plastic off of it and tried to push it down, but it shot right back up to the top. Was a valuant effort, but me thinks I'm screwed.......new gauge needed now?

 

Find out what the gage does when you are cranking the engine.

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Indicating you may have a short to ground under the hood.

 

The guage stays as it is when I crank the engine. I'll try to ground out the wire and see if that helps. Thanks for the suggestions, I'll keep yall posted.

 

anyone remember the part number at autozone for the gauge sending unit? is it the same as the fan switch? It has been a while and I think the sending unit crapped out.

 

The wire that controls the gauge, on the drivers side, is it located near the front of the head?

 

That is the current problem. You need to find where the wire is grounding and fix that.

The gauge should read nominal temp when keyed on and max while cranking the engine. The gauge is grounded through the ignition during crank (does a sweep test to show gauge is working). The gauge reads temp through resistance to ground, created by the sender.

A short to ground somewhere between the sender and gauge will cause the gauge to be stuck maxed out.

There is a single green wire to the sender (drivers cyl head), find it and trace it towards to the bulkhead to see if it may be touching the chassis/engine anywhere. The sender is between the 1 & 3 cyl exhaust ports.

Look on Autozones website.
Being one is a sending unit and the other is a switch, they are not the same.

 

I went into the store and I couldn't find it, neither could the guy behind the counter. Anyone know the part number, because I realize that the fan switch looks the same but has a different function. Help is needed and thanks ahead of time.

 

I'll eat crow..AZ doesn't have them.... for any 90's v8 GM.

STANDARD MOTOR PRODUCTS Part # TS76T, http://www.rockauto.com/

 

Thanks for jacking my thread guys. J/K!!!! My stupid temp. gauge decided it wanted to work again yesterday. It does top out when I crank the engine, then goes back to normal operating temp. But it still doesn't rise above 130 degrees. Weirdest dang thing I've seen in a while. I'll look for a short in the wire and keep yall updated.

 

100° is more like 180° in reality. The 1/4 mark is 200°.
A 195° stat should just be a needle thickness below the 1/4 mark. A 180°, lust above the 100° mark.
Why is is marked 100?... who knows, it's GM. The temp gauge has read the same since they started making them. My '76 suburban read this way (with separate gauge added). My ex-'84 Camaro, my 'bird, the RS, the '71 and the 93Z. The gauge is most reliable/accurate in the 'oh sheet' temp range. Below 220°, it's better used for a reference as things are 'normal'. Similar to ford's temp gauges of being just either hot or, cold.
It's only a small step above being a simple idiot light.

 

Quote:

Originally Posted by Shadyredeyes

it still doesn't rise above 130 degrees

My cars temperature gages read accurately and there’s no reason your’s can’t.

Doesn’t sound like a short - it needs a full test.

You’ll need a 2K potentiometer, an ohmmeter, a large ****, a piece of sheet metal to mount the potentiometer.

After mounting the potentiometer and installing the ****, use the ohmmeter to adjust the potentiometer to read 1370Ω.

Mark the spot on the sheet metal at that point.

Now adjust the potentiometer to 55Ω and mark the spot on the sheet metal at that point.

Now wire the end you had the ohmmeter connected to, . . .to vehicle ground.

At the engine, disconnect the wire that goes to the sensor.

Wire the wiper of the potentiometer to the wire you just removed.

Have these test leads long enuff so you can operate the tester from the cockpit.

Turn the key to RUN.

Set the potentiometer to 1370Ω and observe the gage.

It can take up to a minute for some gages to fully respond to the proper location however your 88 should have the faster responding type.

Does it read 100°?

Slowly sweep the potentiometer to 55Ω and observe the gage.

Is the gage smoothly progressing from 100° to 260°?

If the gage seems notchy then it’s defective and should be replaced.

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Happy Racing!